The Liquid Natural Gas, hereafter “LNG”, production plants currently in the design stages are utilizing economy of scale to increase production with lower capital costs, which has the effect of increasing the power ratings of the critical rotating equipment being supplied. As the power requirements increase with the demand for the next generation of liquefaction plants, the generator size must increase physically. As the generator is the dominant component in terms of rotordynamic stability, the increased size has negative ramifications to the machine reliability. For example, higher power ratings of variable speed hydraulic turbine generators implicitly require larger physical sizes, but the possible loss of generator load demands critical speed separation below continuous speed and above maximum “breakaway” speed. Furthermore, in the design of cryogenic turbine generators and pumps, there limitations on bearing size, shaft diameter and overall diameter of machines of this type. This invention presents a solution for increasing the generator size, and power rating, while still maintaining acceptable rotordynamic characteristics.
For vertical cryogenic turbine generators, power increases of up to 10% can be achieved by reducing the span between the main bearings which offsets the reduction in the critical speed resulting from the increased generator size. However this is not readily accomplished in machines having ball bearings which are cooled and lubricated by the product fluid. This is because the upper main bearing needs to be located outside of the generator end turns to avoid any possible electrical effects associated from the variable speed electrical control system of the generator, and the lower bearing is typically integral to a thrust balancing system which is necessary due to the low viscosity of liquefied hydrocarbon gases. The thrust balancing system is necessary to eliminate the thrust generated by the hydraulic components against the bearings in order to achieve adequate running time between overhauls. The TEMs (Thrust Equalizing Mechanism) mechanisms incorporated in machinery designed by Ebara International Corporation, Sparks, Nev., are good examples of such thrust balancing mechanisms which employ a combination of fixed and variable orifices, but there are limitations with regards to location, length and resultant variable orifice gap size. This invention provides a way for the lower bearing to be disposed closer to the upper bearing, thereby reducing the gap therebetween, without interfering with the thrust balancing mechanism.
U.S. Pat. No. 3,104,553, patented Sep. 24, 1963 to Traeder et al. discloses a mechanical system arrangement for preventing repositioning or mass shift of the components in an assembly due to temperature changes. The patent does not describe hydraulic cryogenic machinery which is the subject the present invention.
U.S. Pat. No. 6,296,765, patented Mar. 8, 1988 to Brown discloses a composite sleeve over a rotor hub with magnets. However, Brown is not related to hydraulic cryogenic machinery. In addition, Brown does not describe the magnetic coupling of the present invention which functions to seal the rotor hub or motor/generator from the hydraulic portion.
U.S. Pat. No. 6,119,553, patented Sep. 19, 2000 to Yamagishi et al. discloses a rotation transmitting device that introduces rotation into a vacuum side space via a flexible meshing type gear drive from an atmosphere side space. Yamagishi et al. is unrelated to hydraulic machinery operated under cryogenic conditions and handling cryogenic liquids.
Other advantages and attributes of this invention will be readily discernable upon a reading of the text hereinafter.